Similar in the way a baker needs to create a list of ingredients to make a cake, list of tools and utensils to be used, there is a need of creation of bill of materials (BOM) for every task. The list of ingredients may comprises of sugar, flour, and butter etc. The list of tools may comprise of mixer, bowls, oven, and pans etc. Making bill of materials enable the bakers not to skip any necessary material required for baking the cake and will buy each ingredient and material. The BOM may also have mention of the place from where to get the materials and ingredients to save time in case if baker sends someone else to buy required materials.
Consider if the customer who came to order cake has to make the list of required ingredients and tools. In the worst case scenario, if the baker had no face to face communication with the customer who came to order the cake. The only way customers told the baker regarding their desired order is list of material they had. The list of material will surely be most likely bill of material also known as BOM. Hence, consider making Printed Circuit Board (PCB) instead of cake. This article has all necessary details of creating a BOM for making hardware such as PCB.
The Definition of BOM
The bill of material (BOM) can be defined as the complete list of material either in raw or mature form, sub-assemblies, assemblies, components, and required tools for manufacturing of a special product such as PCB. The manufacturers are always dependent on the list of material provided in the BOM for the manufacturing of product, therefore the list needs to be sufficiently detailed and highly accurate. The customers are requiring for BOM so as to explain the product’s working. For instance, each electronics product has a BOM for its PCB, in order to know what exactly the circuitry is containing. The assemblers are using the BOM for manufacturing the product with specifications of customers.
Bill of materials is having a major role in the assembly services of PCBs. At RayPCB, we offer BOMs along with fabricated PCBs.
Things to know before creation of BOMs
Creation of BOMs is a time consuming process, therefore skipping it for a while and knowing about certain things which are foremost important. It is a fact that the creation of BOM is time saving process and PCB cost reduction is also possible with chances to reduce mistake in entire process when design of PCBs is complex. Here are certain facts that one must needs to know before creation of BOMs.
1. What is intended to be built? Before thinking of BOM, the design phase of the project intended to be build must have been started, because if you are not familiar with what to be build, then you cannot know about what to cater in BOM. Therefore, compiling information regarding different parts of the intended project e.g. PCB, must be gathered, however the creation of BOM is not possible until and unless complete design of project is ready. Creating a Gerber file will work fine explaining the basic design information of PCB before execution of plan. This is how you will determine the complete list of parts that your BOM may comprise of.
2. Technique for Management of BOM:The creation of BOM is likely to go through multiple changes and more than one person may handle it. Therefore, before getting started with BOM, there is a need for the establishment of a system for its management and to ensure newest version is made use. There is a need for keeping a track of changes and creation of identifiers for various versions. A few capable people should be allowed to edit BOM and responsibility for each individual must be shared for avoiding confusions.
3. Who will be using BOM? As there is a wide range of information that BOM comprises of, therefore multiple departments may use it such as engineering, design, manufacturing, and purchasing etc. while the fabrication of PCBs.
4. What Information needed to be Included in BOM? The categories that are needed to be catered must be included in the BOM at the moment, however specifics are not important. BOM is consisting of basics, for example name of parts and quantity etc. The inclusion of consumables is optional, e.g. bolts and glue etc. If there are any specific suppliers from whom material may be bought should be included in BOM.
5. Organization of BOM: The organization of BOM is going to be helpful before beginning to make it. Therefore, consideration of the number of levels and sub-assemblies are needed to be made, and how many sub-assemblies will be attached to main assembly. Preparing the list for BOM ahead of time is going to be helpful for plugging data in efficient way before actually creation of BOM.
6. Software to be used: Before creating the BOM you need to know which program or software will be used for its creation. More often, BOM is in form of spreadsheet and excel is used for its creation, however any other software may be used. However, the use of advanced software is only made, once the company grows and get more number of orders for PCB fabrication.
The way to begin with writing BOM
By the time, you gathered entire needed information, it’s now time to begin working on the BOM. The process of BOM creation is straightforward. Here is the way to create a detailed BOM.
Creation of Document: Opening the software through which you want to create BOM is the first step. Open excel and create a new spreadsheet. Name the spreadsheet as per your like e.g. BOM but naming it with the intended project is good option.
Organization: Create the levels needed, make the necessary tracking, and create user permissions. Organize the document so as to make it easy for all stakeholders to make changes where needed.
Filling Columns: The columns are to be used for the creation of categories. The titles of each column is comprising of tags e.g. name, part number, and quantity etc.
Filling Rows: The rows are to be filled with information as per category mentioned in column. Each and every component of PCB is having separate row, however make it sure the information is recent most and accurate.
Updating Document: You are required to update the BOM document on regular basis. Whenever some changes are made, you have to update in the BOM list to keep it genuine and keeping the PCB design and fabrication process smooth.
What should be included in BOM?
It depends on essentials of a project that what may be included in the BOM, however in case of PCB design, assembly, and fabrication projects, following is the way to go with.
Portion/Part Number: The manufacturer’s name for the part number must be mentioned in the BOM in case if you want to easily identify the parts. By this, the assembler will be able to use the right component in right place. Each of the part numbers must be unique for avoiding any confusion. International number of parts is crucial for compliance with modern day’s global economy.
Manufacturer’s Name:The name of manufacturer of the parts must also be included in the BOM for finding the right part. In case of PCB manufacturing process, this is more important because most parts are having alike names. Availability of each component is also important, therefore contacting manufacturer ahead of project’s start is vital. It is also significant to ask the manufacturer whether the component will suit your PCB according to your specifications, and also ask for its delivery and cost.
Description:Listing description with each part in the BOM is important e.g. color, dimension, specification, and ratings etc. These details will ensure whether right component is ordered for use. The description must also have the correct units for the measurable parts e.g. ohms, centimeters, and ounce etc. The units must also be consistent throughout the documentation.
Quantity:The quantity of each part must also be fulfilled. In order to avoid shortage, you have to order each component a little more from required quantity so that in case if any part is missed or worn-out, you have next to use.
Type of Procurement:Mentioning the type of procurement in the BOM list will also ensure obtaining the right component. The procurement is describing the way component is bought e.g. whether it is custom made component or is purchased regularly.
Flexibility: The manufacturer of any component is not a problem as far as component serves your needs, however sometimes you may prefer manufacturer on basis of different factors such as price, quality, and feasibility. For example, if a component is produced by two different manufacturers, both have same function, quality, but price is different then you have to go for the one with lesser price. The components need to be flexible, so in case if it’s one manufacturer runs short, you may have it produced by another manufacturer. The process of production of PCB can be made smoother if you have flexibility of the parts. In BOM, some components may be highlighted as critical so as to enable assembler to understand following is mandatory.
Substitute Parts:If there is flexibility possible in regards to the components then you may also include the substitute parts, in case if any requested component is unavailable or any alteration is needed. The substitute part list can reduce loss of time, however the substitute parts must also be justified.
Level of BOM:There are multiple levels of BOM and each level is representing its sub-assembly or assembly. The BOM has its own structure and is divided in to different levels helping the users for easy navigation of the document.
Supporting Files: There are some CAD files, some data sheets of the components, instructions for use, and diagrams etc. which must also be provided with the BOM. The supported documents must be attached along with BOM and provided to those who uses it.
Reference Designator:Each part of the PCB assembly must be designated with a unique reference indicating the exact place on board. Cross referencing of PCB and BOM is also very easy through making the designation same as on the PCB design documentation. The identifiers are of number or alphabets such as R1, P1, and C1 etc.
Type of Package:A small description of the type of package that is being used must also be included in the materials. The packages are for purpose of streamlining production and selection of right package type is making process very cost effective and efficient.
The Method of Placement:Knowing the placement method or SMT ( Surface Mount Technology) is very crucial as it illustrates the description of component which is being attached to the circuit board.
The Board Layer:This category is illustrating the layer of the board on which the component needs to be placed. This category is necessary in case of multi-layered PCBs. The multi-layer PCBs having top, bottom, and other layers.
Footprint/Points:The number of connection points for each component on the board must be notated. The footprints must also be included for each component such as the arrangement of connectors and pads which are connecting them to the circuit board electrically. The footprints and points must be noted for each level of BOM.
Lifecycle/Phase: This comprises of the information of the phase or lifecycle of project. There must be designations in the portion comprising of design, testing, and production. This is assisting in keeping a track of the progress of assembly and creation of realistic timeline for the completion of project.
Notes and Comments:The notes and comments is not of much importance but if you want to make notes for your own convenience. The category may help you to increase the efficacy of the project and complete it within deadlines.
The Example of BOM
Following is the example of BOM containing almost all information mentioned above in detail. You will notice that the BOM sheet is quite clean, clearly labeled, organized, and information is mentioned in a consistent manner. The following example of BOM is illustrating the right and wrong ways of its creation.
In the example above, in correct format you can notice the type of component with its units. The units are consistent throughout the BOM. The additional parameters are further elaborating the components with its percentage difference of values. Package type is also mentioned, next to which is its quantity critical to be known. Moreover, the manufacturer with which these components are available are also given and at the end having comments for personal notes of substitutes. While in the wrong BOM the listing is not proper. The components type and name is not given but only units are given to a few which create confusion. In the additional parameters, proper layout is not followed which cause difficulties in understanding. Packages are not named properly and quantity is also not identifiable. Name of manufacturer doesn’t comply with that of the standard format and comments are missing the values at which the components operates.
The Tips for BOM Creation
The following are some useful tips for the creation of BOM.
1. Style BOM that Suits your Needs: Before the creation of BOM, you must decide what do you require from alliance companies and whether those components are meeting the requirements of PCB design and assembly or not. Each company make BOM in its own way, therefore each project requires to have unique organization of the information and features of project. Customization of BOM as per requirements is needed to be done.
2. Using Template: Every manufacturer of PCBs and assemblers are using templates for BOM for obtaining data from their sales departments before requesting a quotation from alliance companies. The use of template is avoiding problems which are hurdling the make of a creative and effective BOM documentation.
3. Inclusion of Correct Details: The inclusion of correct and helpful details must be catered in the BOM. BOM is playing a critical role in the explanation of assembly and fabrication of PCBs to those who use it. BOM is showing how PCB is made starting from scratch. The consumers may have never communicated with you or may not speak the same language as you, but BOM will make them understand the PCB and its details. Some information is not helpful at all and only create confusion, therefore such information must be neglected. Generally speaking, the more details, the better is BOM.
4. Cross Checking Information: Before you send BOM to the manufacturer or upload it to the website, you have to double check and cross check every information. Every piece of information given in BOM must be correct and should not lead reader to any confusion. Remember that even small mistakes can cause mislead from genuine information, therefore double check before finalizing BOM.
5. Keep Record of Changes: You must manage a system to ensure a constant track of the alteration made in the BOM. You may also create copies of all previous versions of BOM in case if you need to refer to the previous versions. However, make it sure each of the previous versions are clearly labeled and are up to date.
6. Limit Rights of Editing: A number of people would use BOM while the PCB design, assembly, and fabrication is underway, therefore they may attempt to make changes to BOM as per their choices. However, you must limit the rights for making changes or editing to the BOM. The access of editing must be given to specific people only who knows the process of PCB design and fabrication well. Moreover, each person having rights to make changes to BOM should be given an identifier, for instance a specific color for each person so as to know who has made changes.
7. Automation: Try to consider automation for your BOM management. Automation will help you in the identification of discrepancies in the records and may also allow you for increased traceability. It will also enable you to export and import information to different formats. Automation effects are more dominant in the BOM systems which are dedicated and requires purchasing advanced software.
RayPCB Design, Assembly, and Fabrication Services
In RayPCB, special focus and dedication is given to customized PCB manufacturing services. These services comprises of procurement, assembly, and fabrication of PCB. At RayPCB we are making it very easy for your PCB project to be completed within time through our helpful tools and years of experience. You can browse a wide range of our free online resources or even contact us through our support team and we will extend our assistance for the best possible services at any stage of your PCB project.
We are also extending our services for online quote, orders, and re-orders. In case if you have a complete BOM, please feel free to contact RayPCB for a quotation. We also extend our support to create a BOM for your project along with design, assembly, and fabrication of your PCB project.